With the rapid development of urban and rural construction as well as development and utilization of minerals in China, a number of heavy metal pollutants are discharged to environmental water bodies, such as rivers and lakes, and the like. Heavy metals cannot be decomposed in water, are easily combined with other substances, and deposited into sediments at the bottom of the water body under the absorption effects of suspended matters and overlying sediments. The sediments are important parts of the ecological system in the water body, which not only provide nutrients for the organisms in the water body, but also possibly become an interior source for polluting the water body at the same time. Under certain conditions, the heavy metals enriched in the sediments will enter the water body again to cause secondary pollution, which continuously damages the ecological environment of the water body, and is harmful to the human health through a food chain. Therefore, the sediments become important objects for evaluating the pollution level of the heavy metals in the water body and the health status of the water ecological system.
US Environmental Protection Agency proposed a reference value method for risk evaluation of pollutants in ocean and estuary sediments in 1995, which mainly determines risk evaluation low value ERL (Effects range-low) and risk evaluation median value ERM (Effects range-median) according to the mass data of ocean and estuary sediments in North America; however, this method is not applicable to other regions due to territory differences. While the evaluation method for ecological risks of heavy metal pollution in river and lake sediments most widely applied internationally is a potential ecological risk index method proposed by Hankanson (a Swedish scholar), which not only considers the contents of heavy metals in bottom mud, but also associates the ecological effect and environmental effect of the heave metals with toxicology, and a comparable equivalent attribute index grading method is employed for evaluation. Some researches on the aspect of recognizing the ecological risks of heavy metals in sediments of river and/or lake are also developed in China; however, most of these researches use the potential ecological risk index method of Hankanson. Generally, we start these researches relatively late, which are still at the exploration stage.
The potential ecological risk index method of Hankanson is used as a relatively quick, simple and convenient method for dividing the sediment pollution degrees and potential ecological risks of the water body thereof, which obtains an ecological risk value by means of dividing the average concentration by the background value of the heavy metals in the sediments of the evaluated water body, and then multiplying by a toxicity regulation factor, and is a point estimation method. But actually, the concentrations of the heavy metals in the water body sediments may differ largely in different regions and time periods. The indeterminacy attribute and probability characteristics of the risk problems cannot be reflected by relying on the ecological risk value calculated according to the average concentration and the risk level division thereof. Therefore, it needs to develop a risk analysis method which can reflect the concentration fluctuation characteristics of the heavy metals in the water body sediments and the ecological risk probability attributes, so as to provide more scientific and reliable basis for rationally formulating water ecological environment protection measures.